Adhesive agent, method for manufacturing same, filtration material, and air filter

ABSTRACT

An object of the present invention is to provide an adsorbent, a filter medium, and an air filter that have good aldehyde removal performance that undergoes little deterioration over time, where the adsorbent is one in which an inorganic porous medium supports at least an amine-based compound and a compound having a sulfide group as a functional group.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase application ofPCT/JP2021/039438, filed Oct. 26, 2021 which claims priority to JapanesePatent Application No. 2020-182148, filed Oct. 30, 2020, the disclosuresof these applications being incorporated herein by reference in theirentireties for all purposes.

FIELD OF THE INVENTION

The present invention relates to an adsorbent, a filter medium, and anair filter.

BACKGROUND OF THE INVENTION

There is an increasing need for improvement in living environment due toan increase in health and comfort consciousness. There are a widevariety of pollutants in indoor air, and among them, aldehyde compoundssuch as acetaldehyde cause a major problem as pollutants. Acetaldehydeis a typical malodorous component contained in cigarette smoke andexhaust gas from automobiles and has a low odor threshold, which meansthat the odor is likely to be felt even at a low concentration.

Conventionally, activated carbon having a large surface area and a largepore volume is commonly used for removing malodorous components in theair, but the equilibrium adsorption amount of a lower aliphatic aldehydeto the activated carbon is significantly smaller than that of othermalodorous components, and practical performance is not provided.

As a technique for removing a lower aliphatic aldehyde, a method hasbeen proposed in which activated carbon is impregnated with an aminecompound to improve the performance thereof (see Patent Document 1).

On the other hand, a conventional adsorbent has had the problem thatsuch amine compounds are easily oxidized by oxygen in the air, wherebythe effectiveness of the chemical adsorption action for aldehyde isreduced, and the aldehyde removal performance cannot be maintained for along period of time.

In order to solve this problem, a technique has been proposed in whichsilica gel is impregnated with an acid hydrazide compound as an aminecompound and a compound having a thiol group as a functional group as anantioxidant to suppress oxidation of an amine-based compound and tosuppress deterioration over time of aldehyde removal performance (seePatent Document 2).

PATENT DOCUMENTS

-   Patent Document 1: Japanese Patent Laid-open Publication No.    H5-317703-   Patent Document 2: International Publication No. 2015/037483

SUMMARY OF THE INVENTION

However, an adsorbent in which silica gel is impregnated with a compoundhaving a thiol group as a functional group has been confirmed to haveperformance of suppressing deterioration over time, but furtherimprovement in performance has been desired. Accordingly, an object ofthe present invention is to provide an adsorbent, a filter medium, andan air filter that have good aldehyde removal performance that undergoeslittle deterioration over time.

The present invention provides an adsorbent in which an inorganic porousmedium supports at least an amine-based compound and a compound having asulfide group as a functional group.

The present invention also provides a filter medium including theadsorbent of the present invention.

The present invention also provides an air filter including the filtermedium of the present invention.

The present invention also provides a method for manufacturing anadsorbent including dissolving a compound having a sulfide group as afunctional group and an amine-based compound in water, impregnating aninorganic porous medium with the solution, and drying the resultant.

The present invention can provide an adsorbent, a filter medium, and anair filter that have good aldehyde removal performance that undergoeslittle deterioration over time by impregnating an inorganic porousmedium with at least an amine-based compound and a compound having asulfide group as a functional group.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Hereinafter, the present invention will be described in detail. In thepresent invention, “or more” means the same as or more than thenumerical value indicated therein. Further, “or less” means the same asor less than the numerical value indicated therein.

The adsorbent of the present invention includes an inorganic porousmedium. By using the inorganic porous medium, a surface area that cancome into contact with treatment air can be secured, and a sufficientamount of an agent described later can be supported, so that thealdehyde removal efficiency can be enhanced.

As the inorganic porous medium employed in the present invention, oneselected from the group consisting of activated carbon, zeolite,activated alumina, silica gel, activated clay, aluminum silicate, andmagnesium silicate can be preferably used. Two or more selected from thegroup can be used in combination.

Among the inorganic porous media, porous silica is excellent in that itdoes not react with an amine-based compound described later and thatdeterioration of the amine-based compound supported on the porous silicacan be suppressed. In addition, the inorganic porous medium ispreferably porous silica also from the viewpoint that the porous silicais highly hydrophilic, has a high affinity for a water-soluble agentsuch as an amine-based compound, and can further enhance the aldehydeadsorption performance of the adsorbent.

The inorganic porous medium used in the present invention is preferablyparticulate. In the particulate form, it is possible to effectivelyachieve both performance and economy. By using a fibrous inorganicporous medium, the specific surface area increases, the contactefficiency with a target gas increases, and the performance (removalefficiency) is improved, but such a medium is expensive.

The average particle diameter of the inorganic porous medium ispreferably 1 μm or more and 1,000 μm or less. The average particlediameter referred to herein refers to a mass average particle diameterdefined by “Test methods for activated carbon” in JIS K 1474 (2014). Bysetting the average particle diameter of the inorganic porous medium to1,000 μm or less, more preferably 600 μm or less, the adsorption rate ofa lower aliphatic aldehyde gas on the adsorbent can be increased, themanufacture is easy, breakage is less likely to occur because of thegood strength, and generation of dust due to breakage can also besuppressed. On the other hand, when the average particle diameter is 50μm or more, more preferably 100 μm or more, scattering of the inorganicporous medium can be prevented, and handleability and processability canbe improved.

The average pore size of the inorganic porous medium in the presentinvention is preferably 4 nm or more and 50 nm or less. The average poresize in the present invention means a peak diameter obtained by the BJHmethod, and more specifically, the average pore size is determined usingan adsorption-side isotherm obtained by the nitrogen adsorption methodat 77 Kelvin (liquid nitrogen temperature). By setting the average poresize of the inorganic porous medium to 50 nm or less, more preferably 30nm or less, it is possible to increase the specific surface area of theinorganic porous medium while suppressing a decrease in mechanicalstrength of the inorganic porous medium, and the low-boiling aldehyderemoval performance of the adsorbent is further enhanced. In addition,by setting the average pore size of the inorganic porous medium to 4 nmor more, more preferably 5 nm or more, entry of the amine-based compoundand VOC gases into the pores of the granular inorganic porous medium canbe promoted.

The specific surface area of the inorganic porous medium employed in thepresent invention is preferably 30 m²/g or more and 1,000 m²/g or lessin terms of BET specific surface area. By setting the specific surfacearea of the inorganic porous medium to 30 m²/g or more, more preferably50 m²/g or more, the effective area as a reaction field of theamine-based compound supported on the inorganic porous medium isenhanced, and the reaction rate between the adsorbent and the VOC gas tobe removed is enhanced. In addition, by setting the BET specific surfacearea of the inorganic porous medium to 1,000 m²/g or less, it ispossible to suppress a decrease in handleability due to a decrease inmechanical strength of the inorganic porous medium, and it is possibleto suppress unintentional adsorption of the VOC gas, which leads tosecondary odor generation, on the adsorbent.

For the adsorbent of the present invention, it is important that theamine-based compound is supported on the inorganic porous medium.Aldehyde-based odor materials can be effectively adsorbed by theamine-based compound.

It is possible to use, as such an amine-based compound, a primaryamine-based compound such as compounds having amino group(s) includinganiline, an acid hydrazide compound, benzylamine, naphthylamine,cyclohexylamine, (iso)propanolamine, ethanolamine, diethylenetriamine,triethylenetetramine, styrene-ethylamine methacrylate, and styrene-amineacrylate, a monomer, an oligomer, a polymer, or a derivative containingan amino group derived from these compounds.

Amine-based compounds other than primary amine-based compounds, such assecondary amine-based compounds, include azole compounds such as3,5-dimethylpyrazole, 3-methyl-5-pyrazolone, 1,2,3-triazole,1,2,4-triazole, 3-n-butyl-1,2,4-triazole, 3,5-dimethyl-1,2,4-triazole,and 3,5-di-n-butyl-1,2,4-triazole; azine compounds; secondary aminecompounds having alkyl groups such as dipropylamine and dibutylamine;and cyclic secondary amine compounds such as piperidine, piperazine, andpyrrolidine.

In addition, the secondary amine compound preferably has an amide bondor a urea bond in order to prevent re-release of aldehyde compounds.Among them, 1,3-dimethylurea and ethyleneurea are more preferable fromthe viewpoint of high safety, no generation of amine odor, watersolubility, and good processability.

Examples of tertiary amine-based compounds include compounds such asvinylbenzyldimethylamine, vinylbenzyldiethylamine, styrene-diethylamineacrylate, styrene-diethylamine methacrylate, styrene-dimethylamineacrylate, styrene-dimethylamine methacrylate, styrene-ethyldimethylaminemethacrylate, styrene-ethyldimethylamine acrylate,styrene-ethyldiethylamine methacrylate, styrene-ethyldiethylamineacrylate, and triethylamine, monomers, oligomers, polymers, and tertiaryamine-based compounds derived from these compounds.

Among them, a primary amine-based compound having an amino group ispreferable, and among them, an acid hydrazide compound is morepreferable, because the desorption suppression performance forhigh-boiling aldehydes of the adsorbent is further improved.

The acid hydrazide compounds are compounds having an acid hydrazidegroup represented by —CO—NHNH₂ derived from a carboxylic acid andhydrazine, and a nitrogen atom having an unshared electron pair isfurther bonded to the α-position of the hydrazide terminal, whichsignificantly improves the nucleophilic reactivity. The aldehydecompound adsorption performance is considered to be able to be exhibitedbecause the unshared electron pair nucleophilically attacks and reactswith the carbonyl carbon atom of the aldehyde compound and immobilizesthe aldehyde compound as a hydrazine derivative.

Among aldehyde compounds, acetaldehyde has an electron-donating alkylgroup at the α-position of the carbonyl carbon, thus has lowelectrophilicity of the carbonyl carbon, and is hardly chemicallyadsorbed. However, the acid hydrazide compound preferably employed inthe adsorbent used in the present invention has high nucleophilicreactivity as described above and therefore exhibits good chemicaladsorption performance also for acetaldehyde.

In addition, the acid hydrazide compound is preferably a water-solubleacid hydrazide compound from the viewpoint of ease of support treatmenton the inorganic porous medium.

Here, the water-soluble acid hydrazide compound refers to an acidhydrazide compound that is dissolved in water (25° C.) in an amount of0.5 mass % or more.

Examples of the acid hydrazide compound used in the present inventioninclude acid monohydrazides having one acid hydrazide group in themolecule, such as formhydrazide, acetohydrazide, propionic acidhydrazide, and benzoic acid hydrazide, acid dihydrazides having two acidhydrazide groups in the molecule, such as carbodihydrazide, glutamicacid dihydrazide, succinic acid dihydrazide, adipic acid dihydrazide,dodecanedioic acid dihydrazide, fumaric acid dihydrazide, maleic aciddihydrazide, and terephthalic acid dihydrazide, and acid polyhydrazideshaving three or more acid hydrazide groups in the molecule, such aspolyacrylic acid hydrazide.

Among them, carbodihydrazide, succinic acid dihydrazide, and adipic aciddihydrazide are preferably used from the viewpoint of adsorptionperformance. In addition, by using adipic acid dihydrazide, an excellenteffect is exerted particularly on the acetaldehyde adsorption capacity.

The amount of the amine-based compound supported is preferably 0.5 partsby mass or more and 30 parts by mass or less with respect to 100 partsby mass of the inorganic porous medium. By setting the amount of theamine-based compound supported to 0.5 parts by mass or more, morepreferably 2.0 parts by mass or more, it is possible to obtain apractical effect of improving the aldehyde compound removal efficiencyand the aldehyde compound adsorption capacity. On the other hand, bysetting the amount of the amine-based compound supported to 30 parts bymass or less, more preferably 20 parts by mass or less, it is possibleto inhibit the amine-based compound from crystallizing and blocking thepores of the inorganic porous medium, which causes a decrease inadsorption rate and powder fall-off.

In addition, in the adsorbent of the present invention, it is importantthat a compound (hereinafter also referred to as a “sulfide compound”)having a sulfide group (—S—) as a functional group is also supported onthe inorganic porous medium. By doing so, it is possible to obtain anadsorbent in which deterioration of aldehyde removal performance overtime is suppressed. The presence of a metal on the pore surface of theinorganic porous medium and the promotion of the decomposition reactionof the amine compound by the catalytic action of the metal areconsidered to be a main factor of deterioration of the aldehyde compoundremoval performance over time, and this tendency is particularlyremarkable in the case where the amine-based compound is an acidhydrazide compound. On the other hand, it is considered that the sulfidegroup has reactivity with a metal and thus can suppress thedecomposition reaction as described above. Furthermore, since thesulfide group has a property of being easily oxidized, it is consideredthat supporting of the sulfide compound has an effect of preventing theamine-based compound having good reactivity with aldehyde compounds frombeing oxidatively decomposed.

Examples of the sulfide compound used in the present invention includemethionine compounds in addition to dimethyl sulfide and diethylsulfide. Specific examples of the methionine compounds include one ortwo or more selected from L-methionine, D-methionine, DL-methionine,salts thereof, and methionine derivatives such as esters of carboxygroups and amides of carboxy groups contained in these methionines.Among them, methionine is preferable because it is inexpensive and hasgood heat resistance. Among them, L-methionine is inexpensive andpreferably used because it exists in a large proportion in nature.

The amount of the sulfide compound supported is preferably 0.5 parts bymass or more and 20 parts by mass or less with respect to 100 parts bymass of the inorganic porous medium. When the amount of the sulfidecompound supported is 0.5 parts by mass or more, more preferably 1.0parts by mass or more, the sulfide compound can sufficiently react withthe metal component adhering to the pore surface. On the other hand,when the amount is 20 parts by mass or less, more preferably 10 parts bymass or less, it is possible to prevent blocking of the pores of theinorganic porous medium and a decrease in the adsorption rate.

Examples of a method for causing the amine-based compound and thesulfide compound to be supported on the inorganic porous medium includea method in which the amine-based compound and the sulfide compound aredissolved in water, the inorganic porous medium is impregnated with theobtained aqueous solution, and then the inorganic porous medium isdried.

The pH (hydrogen-ion exponent) of an aqueous solution in which 5 g ofthe gas adsorbent of the present invention has been dispersed in 100 gof water having a temperature of 25° C. is preferably 3.0 or more and7.5 or less. The aldehyde compound removal performance is thus improved.Owing to the pH of the aqueous solution being 7.5 or less, morepreferably 6.5 or less, the intermediate produced from the reaction bythe nucleophilic attack on the carbonyl carbon atom of the aldehydecompound by the unshared electron pair of the amine-based compound isprotonated in the acidic reaction field, whereby the intermediatebecomes easy to be dehydrated, so that the immobilization reaction tothe derivative proceeds sufficiently. Thanks to the pH of the aqueoussolution being 3.0 or more, more preferably 4.0 or more, the activity ofthe unshared electron pair of the amine-based compound tonucleophilically attack the carbonyl carbon atom of the aldehydecompound can be sufficiently maintained.

The pH of the adsorbent can be adjusted by causing the adsorbent tosupport at least one acid (hereinafter also referred to as an“organic/inorganic acid”) selected from the group consisting of organicacids and inorganic acids. The organic/inorganic acid is preferably anacid that does not itself generate odor.

Specific examples of the organic acid include adipic acid, succinicanhydride, sulfanilic acid, malic acid, citric acid, and amino acids. Inthe case where the inorganic porous medium is impregnated with adipicacid dihydrazide as the amine-based compound in the form of an aqueousdispersion, adipic acid can be preferably employed. Adipic acid ispreferably used because it keeps the balance of the dispersion of adipicacid dihydrazide stably but does not generate odor or exhibithygroscopicity.

As the inorganic acid, phosphoric acid is preferably used. Phosphoricacid is preferably used because it can form poorly soluble salts withdissolved heavy metals such as iron, which promotes the oxidation ofsulfide groups, and can insolubilize the heavy metals.

As a method for causing the adsorbent to support the organic/inorganicacid, in the case where impregnation with the amine-based compound andthe sulfide compound is performed in the form of an aqueous dispersion,the organic/inorganic acid is preferably added by being mixed with thisaqueous dispersion.

Next, a filter medium of the present invention includes the adsorbent ofthe present invention.

The filter medium of the present invention is preferably formed bysandwiching the adsorbent of the present invention between sheets(hereinafter also referred to as “air-permeable sheets”) having airpermeability.

As the air-permeable sheets, fiber structures are preferable, andspecific examples thereof include cotton-like materials, knitted/wovenfabrics, nonwoven fabrics, paper, and other three-dimensional nets.Laminates of these materials can also be used. By adopting such astructure, it is possible to increase the surface area while ensuringair permeability. From the viewpoint of use as an air filter, a nonwovenfabric is preferably used.

Examples of the fiber forming the air-permeable sheets include naturalfibers, synthetic fibers, and inorganic fibers such as glass fibers andmetal fibers, and among them, synthetic fibers made of a thermoplasticresin capable of being subjected to melt spinning are preferably used.Examples of the thermoplastic resin that forms the synthetic fibersinclude polyester, polyamide, polyolefin, acryl, vinylon (polyvinylalcohol), polystyrene, polyvinyl chloride, polyvinylidene chloride, andpolylactic acid, which can be selected according to the application andthe like. A plurality of types can be used in combination.

The fiber diameter of the fibers constituting the air-permeable sheetscan be selected according to the target air permeability and dustcollection performance in the use as an air filter and is preferably 1μm or more and 2,000 μm or less. By setting the fiber diameter to 1 μmor more, more preferably 5 μm or more, clogging of the surface of thefiber structures with the adsorbent can be prevented, and deteriorationof air permeability can be prevented. In addition, by setting the fiberdiameter to 2,000 μm or less, more preferably 100 μm or less, it ispossible to prevent a decrease in the supporting ability of theadsorbent due to a decrease in the fiber surface area and a decrease inthe contact efficiency with the treatment air.

The basis weight of the air-permeable sheets is preferably 10 g/m² ormore and 500 g/m² or less. By setting the basis weight to 10 g/m² ormore, sufficient strength to withstand processing for making theadsorbent supported is obtained, and rigidity necessary for maintainingthe filter structure when air passes is obtained. In addition, bysetting the basis weight to 500 g/m² or less, more preferably 200 g/m²or less, the adsorbent can be uniformly supported up to the inside ofthe sheets having air permeability, and the handleability at the time ofsecondary processing into a pleated shape or a honeycomb shape is alsogood.

It is preferable that at least one of the air-permeable sheets issubjected to electret treatment. The electret treatment makes itpossible to collect fine dust of submicron size or nano size, which isdifficult to remove normally, by electrostatic force.

As the material to form such an electret air-permeable sheet, materialshaving high electric resistivity, such as polyolefin resins includingpolypropylene, polyethylene, polystyrene, polybutylene terephthalate,and polytetrafluoroethylene, aromatic polyester resins includingpolyethylene terephthalate, and polycarbonate resins, are preferablyused.

In the filter medium of the present invention, the adsorbent ispreferably fixed to the air-permeable sheets using a thermoplasticresin. By using the thermoplastic resin as a binder resin, it ispossible to firmly fix the adsorbent to the air-permeable sheets whilepreventing the adsorbent from being covered with the binder anddeteriorating in the function.

As the thermoplastic resin for immobilizing the adsorbent of the presentinvention on the air-permeable sheets, a thermoplastic resin such asEVA-based, polyester-based, polyamide-based, and low-densitypolyethylene-based thermoplastic resins can be used.

As a method for immobilizing the adsorbent on the air-permeable sheets,a method is preferably used in which mixed powder of the adsorbent ofthe present invention and the thermoplastic resin is scattered on anair-permeable sheet, then another air-permeable sheet is furtheroverlaid, and the product is integrated by hot pressing. By adoptingthis method, it is possible to prevent the surface of the adsorbent ofthe present invention from being covered with the thermoplastic resinand deteriorating in the function, which is advantageous in terms of theadsorption rate, and the adsorbing ability can be extremely effectivelyexhibited.

The amount of the adsorbent supported in the filter medium of thepresent invention is preferably 5 g/m² or more and 300 g/m² or less. Bysetting the supported amount to 5 g/m² or more, more preferably 10 g/m²or more, it is possible to obtain a practical effect of improving thealdehyde compound removal efficiency and the adsorption capacity. Inaddition, by setting the supported amount to 300 g/m² or less, morepreferably 200 g/m² or less, it is possible to prevent the surface of anadsorbent sheet having air permeability from being clogged with theadsorbent and to suppress a decrease in air permeability.

The filter medium of the present invention can also support granularactivated carbon separately from the adsorbent of the present invention.By making the granular activated carbon supported, VOC gases other thanthe aldehyde gas can be removed, and VOC gases can be generally adsorbedand removed.

An air filter of the present invention includes the filter medium of thepresent invention.

As the shape thereof, an original planar shape may be employed, but itis a preferable mode to adopt a pleated shape or a honeycomb shape. Thepleated shape in the use as a direct flow type filter and the honeycombshape in the use as a parallel flow type filter each increase thecontact area of the treatment air to improve the collection efficiencyand simultaneously reduce the pressure loss.

In addition, in a preferable mode, the air filter of the presentinvention is formed by putting the filter medium of the presentinvention in a frame from the viewpoint of air treatment efficiency andhandleability.

EXAMPLES [Measurement Methods]

(1) pH of Adsorbent (Hydrogen-Ion Exponent)

In 100 g of pure water having a temperature of 25° C., 5 g of theadsorbent was immersed, lightly stirred, and then allowed to stand for10 minutes, and the pH of the obtained aqueous solution was measuredwith a pH meter (EcoScan pH 5 manufactured by Lacom). The measurementwas performed three times, and the average value was adopted.

(2) Method for Making Amine-Based Compound and Sulfide CompoundSupported

The inorganic porous medium was impregnated with an aqueous solution inwhich the amine-based compound and the sulfide compound were mixed, andthe resultant was dried to perform adjustment.

(3) Basis Weights of Adsorbent and Thermoplastic Resin Supported (g/m²)

Mixed powder obtained by mixing and stirring the adsorbent and thethermoplastic resin was scattered on a sheet having air permeability,another sheet having air permeability was then overlaid, hot pressingwas performed to perform integration, and the total basis weight wasmeasured. A value obtained by subtracting the basis weight of the twosheets having air permeability from the total basis weight wasmultiplied by the charged amount ratio of each component to determinethe amount of each of the adsorbent and the thermoplastic resinsupported with respect to the entire filter medium.

(4) Acetaldehyde Removal Performance

A flat filter medium measuring 12 cm by 12 cm was attached to anexperimental duct measuring 10 cm by 10 cm, and air with a temperatureof 23° C. and a humidity of 50% RH was sent into the duct at a speed of0.2 m/sec. Further, acetaldehyde (also expressed as C₂H₄O) was added atthe upstream end from a standard gas cylinder at an upstreamconcentration of 10 ppm, and the air was sampled on the upstream anddownstream sides of the filter medium. The acetaldehyde concentrationson the respective sides over time were measured using an infraredabsorption type continuous monitor, and the removal efficiency wascalculated using the following equation.

Removal efficiency (%)=[(C0−C)/C0]×100

Here,

C0: Upstream acetaldehyde concentration (10 ppm)

C: Downstream acetaldehyde concentration (ppm)

The removal efficiency after 100 seconds from the start of addition ofacetaldehyde was taken as the initial removal efficiency. When theinitial removal efficiency of acetaldehyde immediately after preparationof the sample was 40% or more, it was regarded as acceptable.

In addition, the removal efficiency after 100 seconds was measured overtime, and the total amount of adsorption (mass increase (g) of the flatfilter medium) until the removal efficiency decreased to 5% was dividedby the duct area (10 cm×10 cm) and converted to a value per 1 m², whichwas evaluated as the adsorption capacity (g/m²).

(5) Test for Deterioration over Time

In an environment in which the temperature was set to and the humiditywas set to 85% RH, a flat gas adsorption sheet was allowed to stand for3 days after preparation of the sample and then attached to anexperimental duct, and acetaldehyde removal performance was evaluated bythe method described in (4) above.

In addition, the reduction rate of the adsorption capacity through thetest for deterioration over time was calculated using the followingequation.

Reduction rate (%) of adsorption capacity=[((adsorption capacityimmediately after sample preparation)−(adsorption capacity after testfor deterioration over time))/(adsorption capacity immediately aftersample preparation)]×100

In the case where the reduction rate of the adsorption capacity throughthe test for deterioration over time was 50% or less, it was evaluatedas being acceptable.

(6) Heat Resistance Test

In an environment in which the temperature was set to 120° C. and thehumidity was set to 25% RH, a flat gas adsorption sheet was allowed tostand for 1 day after preparation of the sample and then attached to anexperimental duct, and acetaldehyde removal performance was evaluated bythe method described in (4) above.

In addition, the reduction rate of the adsorption capacity through theheat resistance test was calculated using the following equation.

Reduction rate (%) of adsorption capacity=[((adsorption capacityimmediately after sample preparation)−(adsorption capacity after heatresistance test))/(adsorption capacity immediately after samplepreparation)]×100

In the case where the reduction rate of the adsorption capacity throughthe heat resistance test was 50% or less, it was evaluated as being“good”.

[Example 1] (Adsorbent A)

(Inorganic Porous Medium)

As the inorganic porous medium, porous silica (Fuji Silysia ChemicalLtd.) having an average particle diameter of 300 μm was used.

(Amine-Based Compound)

Adipic acid dihydrazide (Otsuka Chemical Co., Ltd.) was used.

(Sulfide Compound)

L-Methionine (manufactured by Wakenyaku Co., Ltd.) was used.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of the sulfide compound in water was mixed withthe inorganic porous medium, and the resultant was dried to prepare anadsorbent A. When 5 g of the adsorbent A was dispersed in 100 g ofwater, the pH was 6.3.

(Air-Permeable Sheet for Upstream Side)

As the air-permeable sheet positioned on the upstream side with respectto the air flow, a chemical bonded nonwoven fabric having a basis weightof 50 g/m² and including 16.5 mass % of vinylon (polyvinyl alcohol)fibers having a single fiber fineness of 1.5 dtex, 22 mass % of vinylon(polyvinyl alcohol) fibers having a single fiber fineness of 7.1 dtex,16.5 mass % of polyethylene terephthalate fibers having a single fiberfineness of 2.0 dtex, and 45 mass % of a phosphorus-based flameretardant-containing acrylic resin binder was used.

(Air-Permeable Sheet for Downstream Side)

As the air-permeable sheet positioned on the downstream side withrespect to the air flow, a charged fiber sheet having a basis weight of20 g/m² and including an electret meltblown nonwoven fabric ofpolypropylene fibers was used.

(Heat Sealing Resin)

Low-density polyethylene (manufactured by Tokyo Printing Ink Mfg. Co.,Ltd., melting point: 98 to 104° C.) was used.

(Manufacture of Filter Medium)

The adsorbent and the heat sealing resin were mixed at a mass ratio of2:1 and stirred until the mixture became uniform, and the mixture wasscattered on the air-permeable sheet for the downstream side, theair-permeable sheet for the upstream side was overlaid thereon, and theproduct was hot-pressed to produce a filter medium A.

[Example 2] (Adsorbent B)

(Inorganic Porous Medium)

The same one as used in Example 1 (adsorbent A) was used.

(Amine-Based Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Sulfide Compound)

Diethyl sulfide (manufactured by Tokyo Chemical Industry Co., Ltd.) wasused.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of the sulfide compound in water was mixed withthe inorganic porous medium, and the resultant was dried to prepare anadsorbent B. When 5 g of the adsorbent B was dispersed in 100 g ofwater, the pH was 6.4.

(Manufacture of Filter Medium)

A filter medium B was produced in the same manner as in Example 1 exceptthat the adsorbent B was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Example 3] (Adsorbent C)

(Inorganic Porous Medium)

The same one as used in Example 1 (adsorbent A) was used.

(Amine-Based Compound)

1,3-Dimethylurea (manufactured by Nacalai Tesque, Inc.) was used.

(Sulfide Compound)

The same one as used in Example 1 (adsorbent A) was

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of the sulfide compound in water was mixed withthe inorganic porous medium, and the resultant was dried to prepare anadsorbent C. When 5 g of the adsorbent C was dispersed in 100 g ofwater, the pH was 6.4.

(Manufacture of Filter Medium)

A filter medium C was produced in the same manner as in Example 1 exceptthat the adsorbent C was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Example 4] (Adsorbent D)

(Inorganic Porous Medium)

The same one as used in Example 1 (adsorbent A) was used.

(Amine-Based Compound)

Carbodihydrazide (manufactured by Japan Finechem Company, Inc.) wasused.

(Sulfide Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of the sulfide compound in water was mixed withthe inorganic porous medium, and the resultant was dried to prepare anadsorbent D. When 5 g of the adsorbent D was dispersed in 100 g ofwater, the pH was 6.5.

(Manufacture of Filter Medium)

A filter medium D was produced in the same manner as in Example 1 exceptthat the adsorbent D was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Example 5] (Adsorbent E)

(Inorganic Porous Medium)

The same one as used in Example 1 (adsorbent A) was used.

(Amine-Based Compound)

Succinic acid dihydrazide (manufactured by Japan Finechem Company, Inc.)was used.

(Sulfide Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of the sulfide compound in water was mixed withthe inorganic porous medium, and the resultant was dried to prepare anadsorbent E. When 5 g of the adsorbent E was dispersed in 100 g ofwater, the pH was 6.4.

(Manufacture of Filter Medium)

A filter medium E was produced in the same manner as in Example 1 exceptthat the adsorbent E was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Example 6] (Adsorbent F)

(Inorganic Porous Medium)

The same one as used in Example 1 (adsorbent A) was used.

(Amine-Based Compound)

Ethyleneurea (manufactured by Nacalai Tesque, Inc.) was used.

(Sulfide Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of the sulfide compound in water was mixed withthe inorganic porous medium, and the resultant was dried to prepare anadsorbent F. When 5 g of the adsorbent F was dispersed in 100 g ofwater, the pH was 6.5.

(Manufacture of Filter Medium)

A filter medium F was produced in the same manner as in Example 1 exceptthat the adsorbent F was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Comparative Example 1] (Adsorbent G)

(Inorganic Porous Medium)

The same product as for the adsorbent A was used.

(Amine-Based Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Substitution for Sulfide Compound)

The sulfide compound was not used, and L-cysteine (manufactured by TomoChemical Co., Ltd.) was used instead.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of L-cysteine in water was mixed with theinorganic porous medium, and the resultant was dried to prepare anadsorbent G. When 5 g of the adsorbent G was dispersed in 100 g ofwater, the pH was 6.5.

(Manufacture of Filter Medium)

A filter medium G was produced in the same manner as in Example 1 exceptthat the adsorbent G was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Comparative Example 2] (Adsorbent H)

(Inorganic Porous Medium) The same one as used in Example 1 (adsorbentA) was used.

(Amine-Based Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Substitution for Sulfide Compound)

The sulfide compound was not used, and L-α-alanine (manufactured byNacalai Tesque, Inc.) was used instead.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of L-α-alanine in water was mixed with theinorganic porous medium, and the resultant was dried to prepare anadsorbent H. When 5 g of the adsorbent H was dispersed in 100 g ofwater, the pH was 6.4.

(Manufacture of Filter Medium)

A filter medium H was produced in the same manner as in Example 1 exceptthat the adsorbent H was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Comparative Example 3] (Adsorbent I)

(Inorganic Porous Medium)

The same one as used in Example 1 (adsorbent A) was used.

(Amine-Based Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Substitution for Sulfide Compound)

The sulfide compound was not used, and succinic anhydride (manufacturedby Nacalai Tesque, Inc.) was used instead.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound and 2 mass % of succinic anhydride in water was mixed with theinorganic porous medium, and the resultant was dried to prepare anadsorbent I. When 5 g of the adsorbent I was dispersed in 100 g ofwater, the pH was 6.5.

(Manufacture of Filter Medium)

A filter medium I was produced in the same manner as in Example 1 exceptthat the adsorbent I was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

[Comparative Example 4] (Adsorbent J)

(Inorganic Porous Medium)

The same one as used in Example 1 (adsorbent A) was used.

(Amine-Based Compound)

The same one as used in Example 1 (adsorbent A) was used.

(Use or Disuse of Sulfide Compound)

No sulfide compound was used.

(Preparation of Adsorbent)

An aqueous solution obtained by dissolving 5 mass % of the amine-basedcompound in water was mixed with the inorganic porous medium, and theresultant was dried to prepare an adsorbent J. When 5 g of the adsorbentJ was dispersed in 100 g of water, the pH was 6.5.

(Manufacture of Filter Medium)

A filter medium J was produced in the same manner as in Example 1 exceptthat the adsorbent J was used as the adsorbent while using the sameair-permeable sheet for the upstream side, air-permeable sheet for thedownstream side, and heat sealing resin as those used in Example 1.

TABLE 1-1 Example 1 Example 2 Example 3 Example 4 Example 5 Example 6Adsorbent used Adsorbent Adsorbent Adsorbent Adsorbent AdsorbentAdsorbent A B C D E F Amine-based compound Adipic acid dihydrazide 5.05.0 — — — — (part by mass) Carbodihydrazide — — — 5.0 — — Succinic acid— — — — 5.0 — dihydrazide Ethyleneurea — — — — 5.0 1,3-Dimethylurea — —5.0 — — — Sulfide compound (part L-Methionine 2.0 — 2.0 2.0 2.0 2.0 bymass) Diethyl sulfide — 2.0 — — — — Other additive component L-Cysteine— — — — — — (part by mass) L-α-Alanine — — — — — — Succinic anhydride —— — — — — pH of adsorbent 6.3 6.4 6.4 6.5 6.4 6.5 Charged basis weightAdsorbent 50 50 50 50 50 50 (g/m²) Thermoplastic resin 25 25 25 25 25 25Supported basis weight Adsorbent 51 51 51 51 51 51 (g/m²) Thermoplasticresin 26 26 26 26 26 26 Immediately after Initial removal 51 51 41 40 4040 production of sample efficiency (%) of C₂H₄O C₂H₄O adsorption 0.310.30 0.16 0.20 0.19 0.16 capacity (g/m²) After test for Initial removal47 42 31 36 34 29 deterioration over time efficiency (%) of C₂H₄O C₂H₄Oadsorption 0.25 0.18 0.10 0.16 0.15 0.09 capacity (g/m²) Reduction rateof 20 40 38 20 21 44 adsorption capacity (%) After heat resistanceInitial removal 51 37 30 38 35 28 test efficiency (%) of C₂H₄O C₂H₄Oadsorption 0.30 0.10 0.09 0.18 0.16 0.09 capacity (g/m²) Reduction rateof 3 67 44 10 16 44 adsorption capacity (%)

TABLE 1-2 Comparative Comparative Comparative Comparative Example 1Example 2 Example 3 Example 4 Adsorbent used Adsorbent G Adsorbent HAdsorbent I Adsorbent J Amine-based compound Adipic acid dihydrazide 5.05.0 5.0 5.0 (part by mass) Carbodihydrazide — — — — Succinic acid — — —— dihydrazide Ethyleneurea — — — — 1,3-Dimethylurea — — — — Sulfidecompound L-Methionine — — — — (part by mass) Diethyl sulfide — — — —Other additive component L-Cysteine 2.0 — — — (part by mass) L-α-Alanine— 2.0 — — Succinic anhydride — — 2.0 — pH of adsorbent 6.5 6.4 6.5 6.5Charged basis weight Adsorbent 50 50 50 50 (g/m²) Thermoplastic resin 2525 25 25 Supported basis weight Adsorbent 51 51 51 51 (g/m²)Thermoplastic resin 26 26 26 26 Immediately after Initial removal 51 4950 50 production of sample efficiency (%) of C₂H₄O C₂H₄O adsorption 0.300.29 0.29 0.30 capacity (g/m²) After test for Initial removal 39 39 2020 deterioration over time efficiency (%) of C₂H₄O C₂H₄O adsorption 0.120.11 0.02 0.01 capacity (g/m²) Reduction rate of 60 63 92 96 adsorptioncapacity (%) After heat resistance Initial removal 36 40 36 36 testefficiency (%) of C₂H₄O C₂H₄O adsorption 0.10 0.12 0.10 0.10 capacity(g/m²) Reduction rate of 67 59 66 67 adsorption capacity (%)

SUMMARY

The acetaldehyde removal efficiency, the adsorption capacity, and thereduction rate of the adsorption capacity of Examples 1 to 6 andComparative Examples 1 to 4 are shown in Table 1.

In all of Examples 1 to 6, since a sulfide compound was used incombination with an amine-based compound, the initial removal efficiencyof acetaldehyde immediately after preparation of the sample satisfied40% or more, and the reduction rate of the adsorption capacity after thetest for deterioration over time also satisfied 50% or less as comparedwith Comparative Examples 1 to 4.

In all of Examples 1, 2, 4, and 5, since an acid hydrazide compound wasemployed as the amine-based compound, the acetaldehyde adsorptioncapacity immediately after preparation of the sample was higher thanthose in Examples 3 and 6.

Furthermore, in both of Examples 1 and 2, since adipic acid dihydrazidewas employed as the amine-based compound, the acetaldehyde adsorptioncapacity immediately after preparation of the sample was 0.30 g/m² ormore, and the initial removal efficiency was 50% or more, which wereparticularly high, as compared with Examples 3 to 6.

Further, in all of Examples 1 and 3 to 6, since L-methionine wasemployed as the sulfide compound, the reduction rate of the adsorptioncapacity after the heat resistance test was a low value satisfying 50%or less as compared with Example 2.

INDUSTRIAL APPLICABILITY

The filter medium using the adsorbent according to the present inventionis preferably used as a filter material for an air filter for cleaningair in a vehicle interior of an automobile, a railway vehicle, or thelike, a filter for an air cleaner used in healthy housing, apet-compatible apartment, an elderly facility, a hospital, an office, orthe like, a filter for an air conditioner, an intake/exhaust filter ofan OA device, a filter for a building air conditioner, a filter for anindustrial clean room, or the like.

1. An adsorbent comprising: an inorganic porous medium; and at least anamine-based compound and a compound having a sulfide group as afunctional group supported on the inorganic porous medium.
 2. Theadsorbent according to claim 1, wherein the amine-based compound is anacid hydrazide compound.
 3. The adsorbent according to claim 1, whereinthe compound having a sulfide group as the functional group ismethionine.
 4. The adsorbent according to claim 1, having a pH of 3.0 ormore and 7.5 or less when 5 g of the adsorbent is dispersed in 100 g ofwater.
 5. The adsorbent according to claim 1, further comprising atleast one acid selected from the group consisting of other organic acidsand inorganic acids, the at least one acid supported on the inorganicporous medium.
 6. The adsorbent according to claim 1, wherein theinorganic porous medium is porous silica.
 7. A filter medium comprisingthe adsorbent according to claim
 1. 8. The filter medium according toclaim 7, wherein the adsorbent is sandwiched between sheets having airpermeability.
 9. The filter medium according to claim 7, wherein theadsorbent is sticked to the sheets using a thermoplastic resin.
 10. Anair filter comprising the filter medium according to claim
 7. 11. Amethod for manufacturing an adsorbent, comprising: dissolving a compoundhaving a sulfide group as a functional group and an amine-based compoundin water; impregnating an inorganic porous medium with the solution; anddrying the resultant.